In the technical area of object position tracking, a tracker or tracking system is a device or structure that determines a position of an object, e.g., in two or three dimensions. A tracking system may also determine an object's orientation, i.e., a direction in which the object is pointing relative to some defined frame of reference. The combination of an object's position and the object's orientation may be referred to as the object's “pose.” Thus, one could say that a pose tracker determines both the position and orientation of an object in three dimensions.
In a similar vein, target tracking relates to determining the position of one or more objects that may be referred to as “targets.” Target tracking is used in a number of applications, from tracking known particles in our solar system, to tracking commercial ships and aircraft at each continent, to tracking players in football and other games. Tracking systems for indoor use may be employed to locate entire objects, e.g., unmanned vehicles or manufacturing and surgical tools, or may be used to track portions of larger objects, e.g., for human motion analysis, etc.
In some cases, object motion is tracked in order to provide input to another system. An example of this is the set of devices currently usable to provide user input to a computing device. For controlling computer programs (games, word processors, CAD programs, geographical information systems, utility programs, etc.), the primary motion-based options today include computer “mice,” touch screens or touch pads, and joysticks.
Computer mice input devices are generally mechanical, opto-mechanical or laser-based optical devices. Such devices typically measure two-dimensional translation of the device on a flat surface. Touch screens and touch pads employ any of a number of technologies to again track a user digit in two dimensions. Exemplary technologies used in such devices include touch resistive technology, multi-touch capacitive technology, multi-touch optical (based on diffraction) and touch wave (acoustic surface) technologies. These techniques all rely on a screen that is covered with a specialized material that enables either single or multi-touch taps and/or drag movements relative to a position on the screen.
The third mentioned technology, joysticks, have been in fairly long and widespread use for interactions with computing devices such as game systems or personal computers. In one example, the velocity of a cursor is controlled with a variable rate by tracking movement of the stick in two dimensions.
In the examples above, the input device is relatively inexpensive, but the control enabled by the device is inherently limited to two dimensions. For tracking in three dimensions, there exist certain free-hand tracking systems based on gyros and accelerometers. For example, an accelerometer can be used to determine acceleration in the vertical direction, and an additional vector magnetometer can be used to determine the magnetic north direction, if there are no magnetic disturbances in the surroundings, to yield orientation information. In theory the acceleration data from the accelerometers can be integrated twice using the orientation information, to determine the relative position of the device.
However, this technique will allow a gradual drift in calculated position relative to the device's actual position, making this combination unsuitable for determining pose. Additional global navigation satellite systems (GNSS) sensors can be used outdoors and ultra-wideband (UWB) systems can be used indoors to stabilize the position to supplement the system described above over large operating volumes.
In another technique, one or more cameras may be used to track a special marker. This system is often used as a benchmark solution due to its high precision. BBC has developed a similar system called free-D for augmented reality, wherein the ceiling is equipped with a number of markers, and an auxiliary camera is mounted on top of a film camera to detect the visual markers. With this system too, accurate pose can be computed. However, such systems, when developed to the point that they provide accurate information, i.e., high precision of pose, are expensive and require fixed installations. Moreover, the update rate is limited by the frame rate of cameras. The latter limitation can be mitigated by using gyros and accelerometers on the tool, however, this will of course increase the already substantial price of the system yet further.
Other systems that attempt to determine pose use an accelerometer and/or gyro together with an IR camera, A row of IR diodes is placed at the screen, and the tool computes its orientation relative to the diodes, given they are in the field of view of the camera. A similar system uses a laser projector placed at the screen that projects a special pattern. An IR camera detects the returned laser reflections, and provides a range image of a part of the surroundings. The 3D image is combined with a standard color camera, and the system can track a number of players and their gestures and movements in three dimensions. However, the orientation of a device cannot be determined with this principle.
One class of systems employs magnetometers. Some such systems measure the magnitude of the magnetic field to calculate a distance to a device, but typically cannot discern the device orientation. Other types of systems require specialized sensor locations or setup. Other systems use a magnetometer in a hand-held tool, which detects its own movement relative to a static magnetic field and wirelessly transmits this data back to the computer. However, this system requires a much more expensive tool. In general, the systems that exist to attempt to track a device either do not perform accurately or do provide high accuracy, but only at a correspondingly high cost in dollars or user effort.
It will be appreciated that this background section was created by the inventors for the reader's convenience, and is meant to discuss problems and solutions noted by the inventors, not to discuss or explain prior art. Thus the inclusion of any problem or a solution in this section is not an indication that the problem or a solution is prior art.